Basing our description on H. R. Rosenberg’s definition, we can describe vitamins as organic compounds required for normal growth and the maintenance of animal life. Animal are unable to synthesize many of these compounds. Vitamins are effective in small amounts. Some are essential for the transformation of energy, but do not themselves supply energy to the body. Finally, somevitamins are essential for the regulation of the metabolism of structural units, but are not themselves used as building units for the structure of the body.
Determination of vitamins in food
Many types of assays are available for estimating the vitamins content of foods. The oldest method, and one which is still used to check all other methods, is the bioassay.
The biological assay. In the mostcommon method of bioassay, groups of animals are first depleted of a vitamin by being fed a diet lacking that substance. Then a series of specific does of the vitamin are administered to the animals, whit each group receiving only one of the does in the series. The animals’ response to intake, in growth and/or other appropriate criteria, is measured and recorded in a standard response curve. Whilethe different groups of animals are receiving known amounts of the vitamin, other comparable groups are fed correspondingly increasing amounts of the vitamin carrier being assayed, and responses of the second set of animals are recorded. The vitamin potency of the carrier is then estimating by comparing the responses of the second set of animals with the standard response curve. Such assays arebased on the assumption that, under comparable conditions, animals will respond similarly to equal amounts of the vitamin. Many criteria are used in this type of assay, but the most common is growth. It may be the growth of a population, an individual, an organ, a tissue, or a cell. The bioassay may also be based on the prevention or cure of some deficiency symptom known of develop in the absenceof the vitamin. The usefulness of biological assays is limited because of their high cost in terms of equipment, labor, and time. Their fundamental advantage is that they give positive proof of biological activity, and thus compounds that are chemically similar to the true vitamin but biologically inactive can be detected with certainty.
The microbiological assay. Assay of this type usemicroorganisms as the test subjects, and require much less time to complete than bioassays using animals. However, they have the disadvantage that the vitamin (or substance suspected of being a vitamin) must first be extracted from its carrier (foodstuff) before being added to the growth medium used for the microorganisms.
The chemical assay. Chemical assays are based on some established chemical property(or properties) of the vitamins. They have definite advantage of being much faster than bioassay, but they must be compared at intervals with bioassays in order to rule out the possibility of assaying as the vitamin any substances that do not function as a vitamin in the body.
Scurvy was already a well-known disease when North America was discovered. Sailors who spent months on thesea almost invariably developed scurvy unless citrus fruits were included in their diet. It was not until the twentieth century, that vitamin C was discovered to be the antiscorbutic factor present in citrus fruits. A dietary deficiency of vitamin C will cause scurvy only in humans, guinea pigs, monkeys, red-vented bulbul birds, and Indian fruit-eating bats. These species are genetically deficientin the enzyme L-gulonolactone oxidase. Other animals are capable of synthesizing the vitamin from glucose via glucuronic acid and gulonic acid lactone. Vitamin C was the first vitamin to be synthesized in the laboratory. Because it is a derivative of hexose, it can be classified as a carbohydrate.
Basando nuestra descripción de la definición H.R. Rosenberg, podemos describir...